A signal analyzer is used for analyzing a signal of a wireless device such as a mobile phone from two viewpoints of time and frequency domains. The signal analyzer converts the analog signal under test into digital data that is digitally processed to produce frequency domain data for example using an FFT.
The signal analyzer is required to have a wider dynamic range and a wider band. The key is to satisfy both wide dynamic range and wide band in the analog to digital conversion.
It is, however, very difficult for an available analog to digital converter to satisfy both a wide dynamic range (=a large bit number) and a wide band (=a high sampling frequency) at the same time. For example, the LTC2242-12, 12-Bit analog to digital (AD) converter manufactured by Linear Technology Corporation, U.S.A., has a sampling frequency of 250 MHz. The LTC2208, 16-Bit AD converter manufactured by the said company has a sampling frequency of 130 MHz. As described, the larger the bit number is, the lower the sampling frequency is in general.
Accordingly, a conventional signal analyzer may have a plurality of analog to digital converters wherein one of them is optimized for a dynamic range and another is done for a bandwidth, or a high sampling frequency, and they are used in parallel. For example, Japanese patent 3,433,724 discloses such an invention.
FIG. 1 is a block diagram of an invention that the Japanese patent No. 3,433,724 discloses. The first path has a narrow band but a wide dynamic range, and the second path has a narrow dynamic range but a wide band.